An impact incident of a vehicle leads to large, positive or negative, accelerations. In connection thereto large forces are created in the vehicle. The vehicle occupants are exposed to the corresponding accelerations and force effects. By the passive protection systems existing in vehicles, mainly seat belts, a large part of the energy will be absorbed, but they principally protect the torso. Collision effects on the neck and head, above the seat belt, thus often lead to great accelerations and considerable damages on the skeleton, muscles and other soft tissues. Many safety systems focus on preventing so called whiplash injuries where movement of the neck and head often causes injuries, when a motor vehicle is hit from the rear. Several systems for preventing such injuries are known. For example, the back of a car seat can be mounted in such a way that the upper part of the seat back or head rest can move forwardly to support the head of the occupant and also in such a way that the seat back can subsequently yield during a rear impact. By those means, the torso of an occupant can be caused to de-accelerate in a more gradual manner, and the head of the occupant can be supported, thus reducing the risk of injury. Examples of this kind of system are disclosed in the international patent applications WO/2008/036005 and WO/2008/115103. Other examples of restraint systems are motorized seatbelt retractors and movable support surfaces, such as knee paddings or systems that provide additional support for bracing a vehicle occupant (see for example WO/2008/041904).
Some recently developed systems are activated in response to a detected crash risk, for instance if the relative position and velocity of another vehicle, as detected by on-board radar for example, indicate that a crash situation is likely or unavoidable. Such systems could also react in response to detected hazardous vehicle dynamic situations, and such situations may be detected by on-board sensors such as accelerometers. Systems for e.g. braking the car as a preparation for an estimated impact are known.
A problem with existing reversible restraint systems is that the systems generally are applied quickly and without warning. Sudden activations of such systems may be uncomfortable and/or alarming for a vehicle occupant. There is also a risk that a restraint system will be removed before the occurrence of a new potentially hazardous situation, or that the use of the restraint system is detrimental for certain impact directions. Moreover, the systems incorporate mechanical solutions and hence can be bulky and also costly for producing and mounting.
A device that intends to prevent personal injury at a car collision by generating a warning signal to occupants to achieve a muscular tensioning is disclosed in the international application WO 97/25630. The warning signal causes a reflex action from the occupants, to tense their muscles in order to absorb the effects of the collision. The device is thus a rather elementary construction and does not, for example, take regard of from where the collision arises.
The object of the present invention is to reduce personal injury at vehicle impact dependent of the nature of the impact.